The present invention relates to an apparatus used to stage the inflation of an airbag in a vehicle occupant restraint system. Inflation of an airbag through the use of gas generators is well known and understood. This invention, a dual stage pyrotechnic inflator (DSP), is a two-stage gas generator used to provide a variable gas output so that the rate of airbag inflation can be controlled. Controlling the rate of gas generation and thereby the rate of rise of pressure within the airbag provides better protection for a wider range of vehicle occupants while minimizing the risk of injury resulting from the airbag deployment. Currently, single stage inflators are designed to inflate rapidly in order to meet required United States Government injury criterion. With single stage inflators, smaller and out of position occupants are at risk of being injured during the airbag deployment. The use of a staged output inflator coupled to the appropriate sensing device reduces the likelihood of injury to the vehicle occupant.
The primary objective of this invention is to supply gas used to fill an airbag in either a single stage or multistage manner. This is accomplished through the use of two combustion chambers in isolation, containing gas generant. Deployment modes may involve deployment of both stages at once or the primary followed by the secondary at some later time to provide the desired gas delivery event.
Controlled inflation of an airbag as taught by Cuevas et al. in U.S. Pat. No. 5,558,367 employs a hybrid inflator containing an inflating fluid and two igniters. The fluid is released by activation of the first igniter. A second igniter is used to ignite combustible material for the purpose of increasing the temperature and pressure of the contained fluid. Buchanan et al., U.S. Pat. Nos. 5,582,428, 5,630,619, and 5,709,406, describe the use of hybrid technology to address the staging problem. The invention describe herein is not a hybrid inflator.
Marchant in U.S. Pat. No. 5,221,109 incorporates into the gas generator, a venting mechanism used to control gas output. Esterberg in U.S. Pat. No. 5,346,254 describes a single combustion chamber inflator design, which employs dual output igniter. The first stage of the igniter provides the ignition impulse required to ignite the gas generant and some point in time later the second stage of the igniter is fired, cracking the gas generant thereby increasing the surface area available for combustion.
Hock in U.S. Pat. Nos. 5,368,329 and 5,398,966 discloses an elongated inflator housing, containing gas-generating wafers spaced along the length of the tube, containing two igniters. The primary igniter provides the ignition source required to ignite the gas generant and the second igniter is used to shatter the wafer when fired at a latter time. Shattering of the gas generant wafer increases burning surface area and thereby the mass generation rate of gas. The DSP does not employ generant shattering technology.
U.S. Pat. No. 5,564,743 to Marchant discloses a multiple stage air bag inflator system wherein the inflator housing contains two separated chambers, each containing gas generating material and an ignition system. The wall that separates the two chambers has a frangible section designed to rupture in response to a predetermined level of gas pressure in one of the chambers, thus providing fluid communication between the chambers.
Faigle et al. in U.S. Pat. No. 5,460,405 describes an apparatus containing a controller and a collision and position sensor for controlling the actuation of the first and second fluid source required to inflate the air bag.
Gioutos et al. in U.S. Pat. No. 5,400,487 discloses a system whereby multiple individual gas generators are used to generate the desired airbag inflation rate. No mention is made of the use of a single staged inflator. Schluter et al. in U.S. Pat. No. 5,839,754 describes a multichambered gas generator and a single ignition source used to ignite the gas generant in the primary chamber. The gas generant in the primary chamber serves as an ignition source for the gas generant housed in the secondary chamber by forcing hot burning gas through bores and into the secondary chambers.